what is "freeze M-TMSI" flag in purge UE Answer Message?

Question

As part of the purge ue procedure, HSS sends PUA-flags within the Purge UE Answer message to the MME or SGSN.
Can someone please explain the importance of bits present in the PUA-flags AVP with respect to the MME or SGSN.

Answer 1

Purge UE Request (PUR) is used to remove a subscriber's data/context when the subscriber is inactive for a long time (days/months maybe).

When MME send PUR to HSS, it responds back with an an indication to freeze the M-TMSI for some time so that same temporary identity can be used when subscriber becomes active.

In the same way, HSS sends freeze P-TMSI indication to SGSN.

PUR-Flag is used to inform the HSS that only the MME/SGSN specific data should be deleted.

Comments

Thank you for your explanation, Ankush Surelia. Do you know when is this TMSI re-used for other user? (How long it will be frozen)

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TMSI is frozen to avoid TMSI double allocation. I am not sure enough if there is a defined time interval for which TMSI will be frozen. But this TMSI can be used for other users during the TMSI allocation procedure which is performed only after a Location Updation Procedure for the purged UE or by Location Cancellation Procedure for the purged UE or in exceptional cases it is freed by the O&M.